In recent years, a demand for a fuel injector used in an internal combustion engine becomes strict due to a strengthened exhaust regulation. Particularly, there is a high interest for expanding a use area and many companies are developing a half lift control capable of improving a minimum injection amount while satisfying a static flow requirement in the past.
The half lift control executes a highly accurate control in a state (hereinafter, referred to as a half lift region) before a valve body provided in the fuel injector completely reaches a valve opening position (hereinafter, a full lift), but a change in injection amount of the half lift region increases due to an individual difference of the fuel injector.
For this reason, various techniques for detecting the individual difference of each fuel injector are proposed. For example, Japanese Patent Application Laid-Open No. 2014-152697 discloses a technique for indirectly detecting the individual difference of the fuel injector, considering a valve opening operation (specifically, a timing in which the valve body opens the valve) of the fuel injector as electric characteristics. Similarly, a valve closing operation of the fuel injector is also detected from the electric characteristics in the known techniques.